The present invention relates generally to a new podiatric surgical procedure and instrumentation. More particularly, the present invention relates to instrumentation and a surgical procedure for endoscopic decompression for Morton's neuroma.
Morton's neuroma is a frequent foot disorder that affects a significant percentage of the people in the United States. Morton's neuroma is a swelling at the bifurcation of one of the digital branches of the plantar nerves. The most common site is in the third intermetatarsal space. Morton's neuromas are also found in the second intermetatarsal space and fourth intermetatarsal space, and rarely in the first intermetatarsal space. In a typical case, the patient experiences sharp pain at the base of the toes, which sometimes radiates into the toes. There can be proximal radiation as well, even as far as the shin. The pain is sometimes described as a burning or "electric shock" sensation. Occasionally, numbness or hyperaesthesia in the toes is present.
The term "neuroma" may actually be a misnomer. Although intermetatarsal neuromas may resemble amputation or "stump" neuromas, the two are different from a histological perspective. Intermetatarsal neuromas are typically characterized by degenerative changes, such as demyelination and wallerian degeneration. Stump neuromas are typically characterized by proliferative changes.
The etiology of Morton's neuroma has been debated in medical literature. T. G. Morton believed that Morton's neuroma was caused by an abnormal metatarsal parabola, a result of pinching of the digital nerves by the metatarsal heads. Betts attributed the cause of the third intermetatarsal neuroma to the fact that the common digital nerve in that interspace received branches from both the medial plantar nerve and the lateral plantar nerve, resulting in a thicker nerve. Nissen felt that the etiology was related to ischemia of the involved nerve. Bossley described the symptoms to be related to inflammation of an intermetatarsal bursa. Gibney believed it to be secondary to flatfoot, while Wachter described how pes cavus feet have an increased incidence of neuromas because of increased tension in the plantar fascia and intermetatarsal ligaments.
Recent evidence points to chronic intermittent trauma being caused by compression and stretching of the common digital nerve. It appears that the transverse intermetatarsal ligament plays a role in this theory. Ground reaction forces create impingement of the neurovascular bundle between the metatarsal heads, because the transverse intermetatarsal ligament does not allow the nerve to move dorsally. Stretching of the nerves occurs during propulsion, as dorsiflexion of the digits stretches it around the rigid intermetatarsal ligament. Graham confirmed this by noting that the characteristic degenerative changes of the nerve occurred just distal to the distal edge of the transverse intermetatarsal ligament.
Treatment of Morton's neuroma has also been the subject of much debate. Various non-invasive conservative care techniques have been tried, such as non-steroidal anti-inflammatory agents, injections of local anesthetics, corticosteroids, orthotic management, padding, strapping and others. However, success with such non-invasive care has been limited.
The medical field has generally adopted two surgical approaches for relieving the pain associated with Morton's neuroma. The first and most common technique consists of resection of the common digital nerve. This procedure can lead to loss of function of the involved nerve and true "stump" neuroma formation. While this type of surgical intervention has a success rate approaching 80%, in some cases the stump neuroma becomes symptomatic post-operatively. This can result in the patient realizing symptoms of pain which are equal, or sometimes worse, than the pain experienced prior to the surgical intervention.
The second approach consists of decompression of the common digital nerve. In mild cases where symptoms are intermittent, the patient is treated by modifying the patient's activities and orthotics. Moderate cases are treated by division of the intermetatarsal ligament through a dorsal approach. Severe cases may add a microsurgical internal neurolysis of the common digital nerve. If pain recurs, treatment for the first recurrence may include a resection of the nerve through a dorsal approach. If a second recurrence occurs, then further resection through a plantar incision and implantation of the proximal aspect of the nerve into muscle may be performed.
Under either of these two surgical techniques, a relatively large incision is made in the foot. The patient typically spends approximately two weeks in a post-operative surgical shoe until sutures are removed. Typically, the patient requires six-eight weeks to become fully ambulatory in normal day-to-day athletic and non-athletic activities.
Accordingly, it is an object of the present invention to provide surgical instrumentation and a surgical procedure to relieve the pain associated with Morton's neuroma and which minimizes the length of time necessary for patient recovery and resumption of normal activities.
Another object of the present invention is to provide surgical instrumentation and a surgical procedure to relieve the pain associated with Morton's neuroma which minimizes the surgical trauma incident to treatment of Morton's neuroma disorder.
These and other objects are attained by the provision of surgical instrumentation and a surgical procedure for relieving the pain associated with Morton's neuroma. First, the patient is prepared and draped in the usual aseptic manner.
Three portal incisions are made. A dorsal incision is made between the metatarsals of the affected interspace on the dorsal aspect of the foot. An interdigital incision is then made between the digits in the interdigital space. Next, a pair of blunt dissecting scissors are inserted into the dorsal incision, and dissection is performed percutaneously between the metatarsal heads. The dissecting scissors are removed, and the metatarsal spreader of the present invention is introduced into the dorsal portal between the metatarsal heads. A small interosseus elevator is then introduced into the interdigital incision to palpate the intermetatarsal ligament from the interdigital portal incision.
The elevator is then placed proximally along the course of the intermetatarsal ligament, inferior, parallel and longitudinal to the direction of the metatarsals, via the interdigital incision. The elevator can then be palpated percutaneously on the plantar aspect of the patient's arch. After the elevator is removed from the interdigital portal incision, a slotted cannula and trocar is introduced through the interdigital incision and into the channel created by the elevator. A proximal incision is made in the proximal aspect of the foot, allowing passage of the cannula and trocar through the skin of the plantar aspect of the foot. The cannula is left in place and the trocar is withdrawn from the slotted cannula. Cotton-tipped applicators can be placed through the cannula in order to remove any adipose tissue which is in the cannula.
The cannula and trocar assembly of the present invention includes a slotted cannula and a trocar. The slotted cannula includes a head at one end, which abuts the handle portion of the trocar. The trocar handle includes a tapered, elongated neck. The head of the cannula is similar in shape to the neck of the trocar and allows the trocar and cannula assembly to be positioned between the digits of the foot.
Next, an endoscope is placed in the proximal portal of the slotted cannula, which allows visualization of the intermetatarsal ligament, as well as the lumbrical tendon. A lumbrical hook is then inserted into the distal portal of the cannula. The lumbrical hook of the present invention includes a handle and an insert which is releasably secured by the handle. The insert includes a bend at one end which enables the insert to be secured within the handle. Opposite the bend, the insert includes a hook, which can be used to engage the lumbrical tendon. Using the hook, the lumbrical tendon is brought to one side of the slotted cannula, exposing complete visualization of the intermetatarsal ligament. A hook knife is then used to engage the intermetatarsal ligament from proximal, and a retrograde motion at the distal end of the cannula allows for severance of the intermetatarsal ligament.
The endoscope can be removed and placed in the distal portal of the cannula, allowing visualization of the proximal aspect of the intermetatarsal ligament. If there are any remaining fibers, these are then released using the hook blade. At this time, complete visualization of the severance of the ligament may be achieved, assuring completion of the surgery. The slotted cannula is copiously lavaged with sterile saline to remove any cotton fibers left behind.
Prior to closing the incisions, the intermetatarsal elevator can be placed into the interdigital portal incision, and allowed to pass between the metatarsal heads freely without impedance by the intermetatarsal ligament. This assures that a complete release of the intermetatarsal ligament has been achieved. The portal incisions are then closed in a standard manner. A sterile compressive gauze dressing is then placed on the patient. The patient is allowed to ambulate immediately.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.